The present invention relates to subterranean treatment operations, and more particularly, to improved treatment fluids comprising pumicite, and methods of using these improved treatment fluids in subterranean formations.
Treatment fluids are used in a variety of operations that may be performed in subterranean formations. As referred to herein, the term “treatment fluid” will be understood to mean any fluid that may be used in a subterranean application in conjunction with a desired function and/or for a desired purpose. The term “treatment fluid” does not imply any particular action by the fluid. Treatment fluids often are used in, e.g., well drilling, completion, and stimulation operations. Examples of such treatment fluids include, inter alia, drilling fluids, well cleanup fluids, workover fluids, conformance fluids, gravel pack fluids, acidizing fluids, fracturing fluids, spacer fluids, and the like.
Spacer fluids often are used in oil and gas wells to facilitate improved displacement efficiency when displacing multiple fluids into a well bore. For example, spacer fluids often may be placed within a subterranean formation so as to physically separate incompatible fluids. Spacer fluids also may be placed between different drilling fluids during drilling-fluid changeouts, or between a drilling fluid and a completion brine.
Spacer fluids also may be used in primary or remedial cementing operations to separate, inter alia, a drilling fluid from a cement composition that may be placed in an annulus between a casing string and the subterranean formation, or in the wellbore or inside a casing string, whether the cement composition is placed in the annulus in either the conventional or reverse-circulation direction. The cement composition often is intended, inter alia, to set in the annulus, supporting and positioning the casing string, and bonding to both the casing string and the formation to form a substantially impermeable barrier, or cement sheath, which facilitates zonal isolation. The cement composition may also set inside the casing or inside the wellbore. If the spacer fluid does not adequately displace the drilling fluid from the annulus, or the cement slurry does not adequately displace the spacer from the annulus, the cement composition may fail to bond to the casing string and/or the formation to the desired extent, or pockets of drilling fluid and/or spacer fluid may be left which could compromise the hydraulic isolation. In certain circumstances, spacer fluids also may be placed in subterranean formations to ensure that all down hole surfaces are water-wetted before the subsequent placement of a cement composition, which may enhance the bonding that occurs between the cement composition and the water-wetted surfaces.
Conventional treatment fluids, including spacer fluids, often comprise materials that are costly and that, in certain circumstances, may become unstable at elevated temperatures. This is problematic, inter alia, because it may increase the cost of subterranean operations involving the treatment fluid.
Treatment fluids comprising vitrified shale may contain crystalline silica. For example, vitrified shale may contain about 16% crystalline silica and amorphous silica Crystalline silica is an inhalation hazard and can lead to health problems, such as silicosis, with extended exposure.